Astronauts explore a new world in Interstellar. Photo: Paramount/Warner Bros.
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Near-light speed travel increasingly impossible, according to maths

Travelling at close to the speed of light may be necessary for humans to colonise the galaxy, but the maths show it'd be like flying through a cloud of bombs - but also that we should notice the explosions here on Earth, if any other civilisation has managed the feat.

The sci-fi blockbuster Interstellar depicts a dilapidated Earth too tired to support life anymore. To survive, mankind sends a team of researchers on a spaceship through a wormhole to find a new home in another galaxy, thus preserving possibly one of the rarest things in the universe – intelligence. This sounds fanciful, but it could happen in real life  engineers say that future technologies may make a spacecraft capable of interstellar travel possible.

No matter how badly we treat the planet, the Sun will be responsible for its ultimate destruction. After roughly one billion years the Sun will have grown into a red giant, and the gradual increase in temperature will have wiped clean the Earth’s surface. There are three options (assuming our species isn’t extinct before then): 1) sit and twiddle our thumbs until we are fried to death; 2) move the Earth far away from the Sun (which would bring a different set of problems); or 3), find a new home.

It seems the third option is the only ideal choice we have. We'll have to start building interstellar spacecraft eventually, and the lenient deadline of one billion years should give us enough time to do so. Fairly straightforward calculations tell us spacecraft capable of travelling at a significant fraction of the speed of light is possible - in so-called "relativistic spacecraft"  with enough time for technological advancement, and, of course, money.

There are of course plenty of challenges, though, and Ulvi Yurtsever and Steven Wilkinson from defence contractor Raytheon outline one which until now has been overlooked. In a paper published in arXiv, they say that any object travelling at relativistic speeds will interact with photons in the cosmic microwave background (CMB), creating a drag that results in slower travel.   

The CMB is the afterglow of the Big Bang, present in every direction that we point our telescopes as a faint light occupying the microwave part of the electromagnetic spectrum. Each cubic centimetre of the cosmos has over 400 microwave CMB photons, so any spacecraft moving through these would have a difficult time avoiding them. It would be like trying to dodge a swarm of flies on the driveway; you will get some goo on your windshield. And in this case plenty – trillions per second for a spacecraft moving at significant fractions of the speed of light.

Particle physics dictates that if the energy involved in a collision between an atom's nucleus and a microwave photon is high enough, electron-positron pairs can be created. An electron-positron pair is when a high energy photon (a packet of energy) interacts with a heavy nucleus to form a positively charged electron – a positron.

Yurtsever and Wilkinson describe how CMB photons will appear, from the perspective of the spacecraft travelling close to the speed of light (known as its "rest frame"), as highly energetic gamma rays that have a range of effects. If those photons interact with the material of the spacecraft hull, the effects will range from ionisation to "Compton scattering"  the scattering of high energy photons from a charged particle at rest, which in this case means further gamma rays, creating electron-positron pairs. Each time one of these pairs is formed, it creates a massive amount of energy - as much as 1.6 x 10-13 joules per pair. This doesn’t seem like a lot, but a spacecraft can collide with trillions of CMB photons per second. Assuming an effective cross-sectional area of, say 100 square metres, the effect is about 2 million joules per second across the face of the ship. That's roughly equivalent to the energy released when half a kilo of TNT explodes, every second.

Things also get more complicated when taking time dilation into account. Seconds last longer when something travels nearly as fast as the speed of light, relative to something travelling at a slower speed, so our theoretical spaceship will take longer to disspiate the energy that builds up on its front  increasing the effective energy hitting it per second to somewhere in the order of 1014 joules, or a little bit more energy than that released by the atomic bomb which fell on Hiroshima.

So, travelling at almost the speed of light will obviously have a huge drag effect. Yurtsever and Wilkinson write that a way to overcome the issue would be to keep the spacecraft’s velocity below the threshold for electron-positron pair creation, thus reducing drag and energy dissipation. That threshold is crossed as the spacecraft reaches 99.9999999999999967 per cent of the speed of light, so it's still a relatively high velocity.

There's an interesting side effect to all this, though  any relativistic spacecraft like this will bounce into so much of the CMB, it'll scatter it in a way that produces a unique light signature. "As a baryonic spacecraft travels at relativistic speeds it will interact with the CMB through scattering to cause a frequency shift that could be detectable on Earth with current technology," write Yurtsever and Wilkinson. In other words, if we know what to look for, we should be able to spot the interstellar contrails of near-light speed spaceships.

They actually calculate the properties of this signature  it should take the form of radiation in the terahertz to infrared regions of the electromagnetic spectrum, and it should also be moving relative to the rest of the CMB. If relativistic spacecraft are darting through the cosmos, this kind of signature should be visible using current astrophysical observatories.

However, Yurtsever and Wilkinson also look at what would happen to such a ship if it hit anything bigger than a photon  like, say, a grain of dust. Collision with an object as tiny as 10-14 grams would have an impact energy close to 10,000 megajoules, which makes it clear that any relativistic spacecraft would need a clear runway before it can take-off to a new land for the sake of humanity. Or perhaps this is just yet more evidence that, like the crew in Interstellar, jumping between wormholes is a better bet.

Tosin Thompson writes about science and was the New Statesman's 2015 Wellcome Trust Scholar. 

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We're asking the wrong questions about the Google “anti-diversity memo”

Which sex is better at what skills is less important than which skills we value in the first place. 

Yes, I feel sorry for the Google employee who has been fired for writing an "anti diversity manifesto" and circulating it within the company. (Guess what? It leaked.) Losing your job is painful, and doing it in public is even more so. But the conversation around this is heading in such an unproductive direction (do women suck at maths?) that I can't resist wading in.

I agree with the writer that these issues are hard to talk about, but that pushback comes from both directions. Look at the crap Mary Beard is wading through for trying to inject some facts into a discussion about the racial composition of Roman Britain. Nicholas Nassim Taleb keeps honking about "diversity genes" and refusing to listen to evidence that contradicts him. But in his mind, he's Mr Science - sorry, Professor Science - and she's Madam Arts-Subject.

This matters, because when it comes to diversity, there are fact-based positions on both sides. Yet there is a certain strand of Rational Internet Thinker (let's be honest, mostly men) who solemnly tells everyone that we Must Stick To The Facts while advancing deeply ideological stances, which only happen to look "natural" because they are so embedded in our culture. 

But back to the subject at hand. Here's the recap: the memo was headlined  "Google’s Ideological Echo Chamber" and its writer's firing will be taken as confirmation that his thesis was true. Ironically, this will be done by the same section of the right which usually has no problem with firing at will and normally thinks that HR should be a brutally Darwinian process. (Looked at from that perspective, of course Google would fire someone who brought such criticism on the company.) But now there are Principles involved. Probably Free Speech is under attack. Political Correctness may even have Gone Mad. Social Justice Warriors are on the march. Before it's all placards as far as the eye can see, instead I would like to look at what was actually said, and whether it's an argument with any merit. 

In essence, the memo argued that the gender imbalance of staff in tech companies like Google is primarily the result of biological, not cultural differences. ("They’re universal across human cultures," it argued. "They often have clear biological causes and links to prenatal testosterone".) There are differences in ability between the sexes, the writer said, and that's why most top programmers are men. Men like numbers, and the numbers like them right back.

The memo added:

Differences in distributions of traits between men and women may in part explain why we don’t have 50% representation of women in tech and leadership. Discrimination to reach equal representation is unfair, divisive, and bad for business.

The section about typically female traits is also interesting, because of a couple of points the writer picks out.

"Women, on average, have more...

- Openness directed towards feelings and aesthetics rather than ideas. Women generally also have a stronger interest in people rather than things, relative to men (also interpreted as empathizing vs. systemizing).

- These two differences in part explain why women relatively prefer jobs in social or artistic areas. More men may like coding because it requires systemizing and even within SWEs, comparatively more women work on front end, which deals with both people and aesthetics.

- Extraversion expressed as gregariousness rather than assertiveness. Also, higher agreeableness. This leads to women generally having a harder time negotiating salary, asking for raises, speaking up, and leading. Note that these are just average differences and there’s overlap between men and women, but this is seen solely as a women’s issue. This leads to exclusory programs like Stretch and swaths of men without support.

- Neuroticism (higher anxiety, lower stress tolerance).This may contribute to the higher levels of anxiety women report on Googlegeist and to the lower number of women in high stress jobs.  

Well, SOMEONE has been reading their Simon Baron Cohen. The first point is a distillation of Baron Cohen's argument about "male brains" being better at understanding systems, and "female brains" being better at feelings - which he extends to say that autistic traits might be an "extreme male brain". Unsurprisingly, there are other scientists in the field, such as Cordelia Fine and Rebecca Jordan-Young, who find a lot of the neuroscience of sex difference quite flaky.

I'm not a neuroscientist, but from a lay perspective, my take is that yes, there are some biological differences between the average male and female brain, but that these pale beside a) the way our brain architecture is shaped by stimuli (like years of being told you're rubbish at maths) and b) the overall effect of culture (eg companies which value presenteeism, or make it hard for women to return after having children, or cover up for senior men who are repeated sexual harassers etc etc). 

The "higher agreeableness" point was dealt with by Sheryl Sandberg in Lean In. Women aren't stupidly not asking for raises or being assertive in the office because they are delicate little flowers. One of the reasons they are more agreeable at work is because they face heavier penalties if they are not. As Sandberg formulates it: "Success and likeability are positively correlated for men and negatively for women. When a man is successful, he is liked by both men and women. When a woman is successful, people of both genders like her less.” Women are nicer because there are more negative consequences for them if they are not nice.

The last point about neuroticism is bleakly funny, because while women might report more anxiety, men commit suicide in far greater numbers. Which gender is really more susceptible to stress and anxiety? Women talking more about their mental health on "Googlegeist" is being held against them here, when possibly one of the reasons that more men kill themselves is because of the stigma of talking about their feelings.

Overall, the memo makes some compelling points, but it also chucks in a lot of stuff that "everyone knows" about sex differences, which isn't scientifically supported, and also some evolutionary psychology about "protecting females" which strays into the kind of rhetoric found on MRA sites. Its understanding of male and female work patterns can also be naive, for example:

"Yes, in a national aggregate, women have lower salaries than men for a variety of reasons. For the same work though, women get paid just as much as men. Considering women spend more money than men and that salary represents how much the employees sacrifices (e.g. more hours, stress, and danger), we really need to rethink our stereotypes around power."  

I mean, doesn't this just raise a huge number of questions?

How often do men and women do the same work, and for what reasons might they not? (Clue: women do far more unpaid care work and housework.) Are women spending that money on themselves, or are they running household budgets, which is an unpaid project-management task they are doing alongside any paid work? What an individual finds stressful is also entirely subjective.

The author chucks in a reference to "Marxist intellectuals" but doesn't seem to have read any of the vast and fascinating literature on unpaid care and its interaction with paid work. I'd recommend starting with The Second Shift or Wife Work. Angela Saini's Inferior is a good recent choice, too, on women's overlooked contributions to science.

When I talk about feminism with self-styled rationalist men, this dynamic comes up again and again. They will present my arguments as mere anecdote and emotion, which - sad shake of the head - is contradicted by the available evidence. When you point to peer-reviewed studies, or great ethnographies, supporting your point, which they haven't bothered to read, they steam on regardless. It makes the contest deeply unequal. Internet skeptic types talk about the need to engage with writers they don't agree with, and the importance of free and open debate, but often actually don't want to read the contrary view. 

 

***

If you want to read more about the discussion of the science of sex differences which has arisen as a result of this memo, then this piece by Slate Star Codex is interesting - it argues that interest in STEM subjects, not ability, might be the key difference between the sexes. It also completely misses the point. 

Here's a thought experiment. Say you were recruiting for a spoon-juggler. Your advert would probably mention "needs to juggle spoons". But, almost certainly, there would be other skills involved. Turning up to performances on time. Keeping your spoon inventory in check. Not turning up drunk. Not stealing forks from the fork-juggler. 

This is what the argument that women can't succeed in tech because they are innately bad at the skills needed to succeed in tech sounds like to me. We know that many of the early programmers were women, back when the job was considered to be largely secretarial. (Go watch Hidden Figures for more on this, and also because it's just a lovely film and I am so happy for Mahershala Ali and Taraji P. Henson.) We know that the fastest way to depress wages in a job is to feminise its workforce. It's not unreasonable to wonder if we've constructed the whole idea of "success in tech" in such a way that it makes men's success look natural and pre-ordained. Yes, you need to be able to code to be a coder. But there are other skills you need too. 

Yonatan Zunger, who recently left Google, makes this argument better than I could. And he seems to own a pair of testicles, so you know he's more rational and objective than me:

"Essentially, engineering is all about cooperation, collaboration, and empathy for both your colleagues and your customers. If someone told you that engineering was a field where you could get away with not dealing with people or feelings, then I’m very sorry to tell you that you have been lied to. Solitary work is something that only happens at the most junior levels, and even then it’s only possible because someone senior to you — most likely your manager — has been putting in long hours to build up the social structures in your group that let you focus on code.

All of these traits which the manifesto described as “female” are the core traits which make someone successful at engineering. Anyone can learn how to write code; hell, by the time someone reaches L7 or so, it’s expected that they have an essentially complete mastery of technique. The truly hard parts about this job are knowing which code to write, building the clear plan of what has to be done in order to achieve which goal, and building the consensus required to make that happen.

All of which is why the conclusions of this manifesto are precisely backwards. It’s true that women are socialised to be better at paying attention to people’s emotional needs and so on — this is something that makes them better engineers, not worse ones."

As I said on Twitter, this is a pattern we see again and again - a high status job is coded as "male", requiring "male" traits, to justify men's dominance of it. The same thing happens in politics: we are assured that politicians need to be "strong" and "decisive", when many of the most successful male politicians today have incredible people skills. Jeremy Corbyn makes time for everyone he meets, hugging them and posing for endless selfies. Sadiq Khan has that Queen Mum ability to remember your name and a key fact about you. What's the real difference between the Clintons? Bill demonstrated huge empathy and made people he was talking to feel special; Hillary didn't. But still, maybe men dominate politics because they are just more aggressive and ambitious. Yeah, OK. 

Tech suffers from a similar silent rewriting of core competencies to flatter its mostly male leaders.

We have all these conversations about how hard it is for Mark Zuckerberg to make the leap to being a frontman CEO because he's a maths guy, not a people guy. We treat this like he's doing an amazing project of personal growth. We don't go, "wow, they really lowered the bar for CEOs to let someone without some of the key skills have a go at it". Or, "his poor colleagues, having to make up for the stuff he's not naturally gifted at". 

There was a similar reaction when Sergey Brin and Larry Page brought in Eric Schmidt when it was time for Google to "grow up". We didn't say, "How embarrassing, they have to find someone to counteract their deficiencies." We said: "Smart move. Not every human can possess all skills, it's wise to have a range of experience and aptitudes at the top of your company."

So this, for me, is the most interesting takeaway from the Google memo. "Do women suck at maths" is a complicated question, and I'm not sure how far answering it will move the conversation forwards. "Have we structured society so that those competitions between the sexes that men can win are deemed to be the most important competitions?" is a better one.

Helen Lewis is deputy editor of the New Statesman. She has presented BBC Radio 4’s Week in Westminster and is a regular panellist on BBC1’s Sunday Politics.